Containment in international relations refers to a foreign policy strategy aimed at preventing the spread of an adversary's influence or ideology. This strategy was most notably used by the United States during the Cold War to limit the expansion of Soviet communism. The idea behind containment was to "contain" the spread of Soviet influence by establishing military and political alliances and by providing economic and military assistance to friendly countries. The goal of containment was to prevent the Soviet Union from expanding its sphere of influence and to promote stability and security in regions of strategic importance.
Source: Gaddis, J. L. (1997). We Now Know: Rethinking Cold War History. Oxford University Press.